1. Field of the Invention
The present invention relates to an image display apparatus and a control method for same.
2. Description of the Related Art
Broadly speaking, backlights for liquid crystal display apparatuses are referred to either as edge-lit (side-lit) or direct-lit systems. Edge-lit systems involve light sources arranged at the periphery of a light guide panel disposed at the rear of a liquid crystal panel, and direct-lit systems involve light sources arranged at the rear of a liquid crystal panel such that the liquid crystal panel is illuminated directly from the rear surface. In general, both types of backlight are composed as a single backlight unit by combining several light sources into a light source block, and then combining a plurality of these light source blocks.
Here, if the light sources in the backlight are light-emitting diodes (called, “LED” below), then a light source drive circuit is connected to each light source block, and a constant current is passed through the light source drive circuit, thereby causing the LEDs to emit light. However, since there are individual differences in the brightness and chromaticity of the LEDs, then brightness unevenness (non-uniformities) and color unevenness (non-uniformities) occur in the backlight when the same current is passed through all of the light source blocks. Therefore, in order to suppress brightness unevenness and color unevenness, it is common to adjust the LED drive conditions of the respective light source blocks before shipping the product.
Furthermore, in response to change in the brightness of a LED as a result of deterioration over time or temperature change arising after product shipment, it is common for brightness unevenness and color unevenness in the backlight to be suppressed by determining a brightness change amount by a brightness detection circuit and adjusting the LED drive conditions in accordance with the brightness change amount.
One example of a processing method for suppressing brightness unevenness caused by deterioration over time of a LED of this kind is the technology described in Japanese Patent Application Publication No. 2008-310147. In Japanese Patent Application Publication No. 2008-310147, in an edge-type backlight, the display region of the liquid crystal panel is divided into a plurality of regions, the brightnesses of the respective regions are measured, and distribution data indicating a distribution of the brightness is detected from the measured brightness information. The gradation of the image signal is then adjusted on the basis of the distribution data, and the amount of light from the backlight is controlled on the basis of this distribution data and the image signal.
According to Japanese Patent Application Publication No. 2008-310147, if the brightness distribution when the LEDs are lit can be approximated to a Gaussian distribution, then brightness unevenness caused by deterioration over time of the backlight can be eliminated by controlling the amount of light of the backlight on the basis of the brightness distribution and the image signal.